The present invention relates to an optical disk device which performs recording, replay, or deletion upon an optical disk which has a plurality of information recording layers, and in particular relates to such an optical disk device which performs layer jump.
From the past, optical disk devices which perform recording, replay, or deletion of information upon such optical disks have been generally widespread. These optical disks may be, for example, single sided two-layer type Blu-ray disks.
It is necessary for such a prior art type optical disk device to read out information recorded upon each layer of an optical disk (i.e. on both the first layer and the second layer) from that optical disk. Due to this, such a prior art type optical disk device transits from a state in which its pickup is reading out information recorded on the first layer to a state in which the pickup reads out information recorded on the second layer. In order to do this, such a prior art optical disk device performs so called “layer jump” operation. This “layer jump” is an operation in which the prior art type optical disk device applies a jump pulse, consisting of a kick pulse and a brake pulse, to an actuator, so as to drive an objective lens in the direction to approach the objective lens to an information recording surface of the optical disk, or in the opposite direction to withdraw the objective lens from the information recording surface. Corresponding to the change of the relative distance between the objective lens and the information recording surface of the optical disk which accompanies this shifting of the objective lens by the actuator, the output value of the FE signal follows a graph like that shown in FIG. 1A, which consists of two curves.
FIGS. 1A through 1D are figures showing the waveforms of the focus error signal (hereinafter termed the “FE signal”) and the jump pulse during layer jump, for an optical disk device according to the prior art. With the layer jump described above, generally, the timings at which the kick pulse and the brake pulse are applied are controlled on the basis of the level of the FE signal shown in FIG. 1A.
To explain this matter in detail with reference to FIGS. 1A and 1B, when from the state in which focus servo control is being performed upon the first layer, the level of the FE signal becomes greater than a kick start threshold value KS, then this prior art optical disk device starts the application of a kick pulse to the actuator. Due to this, the objective lens is driven so as to accelerate in the direction to approach the objective lens towards the information recording surface of the optical disk, or in the opposite direction to withdraw the objective lens from the information recording surface. And, when the level of the FE signal becomes lower than a kick end threshold value KE, then this prior art optical disk device terminates the application of the kick pulse to the actuator. Due to this, the acceleration of the motion of the objective lens is terminated so that it transitions to motion at uniform speed, and it passes along an indeterminate section over which the FE signal is not outputted.
And, when the level of the FE signal becomes less than a brake start threshold value BS, then this prior art optical disk device starts the application of a brake pulse to the actuator. Due to this, braking is applied to the motion of the objective lens in the opposite direction to that of its motion at uniform speed. And, when the level of the FE signal becomes greater than a brake end threshold value BE, then this prior art optical disk device terminates the application of the brake pulse to the actuator. Due to this, the acceleration of the motion of the objective lens is terminated. Subsequently, this prior art optical disk device performs focus servo control upon the second layer of the disk.
A layer jump is executed with the above type of flow. In this manner, such a prior art type optical disk device transits from a state in which its pickup is reading out information recorded on a first layer of a disk, to a state in which the pickup reads out information recorded upon the second layer of the disk.
It should be understood that, in Japanese Laid-Open Patent Publication 2000-242933, there is proposed a pickup device which applies an offset voltage to the FE signal when the reading layer of the optical disk is changed.
However, sometimes it happens that a so-called inter-layer offset occurs over the indeterminate section shown in FIG. 1A. This inter-layer offset depends upon the adjusted value of an offset voltage which is applied in order to cancel offset of the FE signal. For example, if the FE signal is offset adjusted in the + direction, then an inter-layer offset of the form shown by the double-dotted broken line in FIG. 1A is generated in the intermediate section described above. In a similar manner, if the FE signal is offset adjusted in the − direction, then an inter-layer offset of the form shown by the single-dotted broken line in FIG. 1A is generated in the intermediate section described above.
When an inter-layer offset such as shown in FIG. 1A is generated in the intermediate section described above, then, when the offset is being adjusted in the + direction, the timing at which the application of the brake pulse is started becomes unduly early, which is undesirable. (Refer to FIG. 1C.) In a similar manner, when the offset is being adjusted in the − direction, the timing at which the application of the kick pulse is terminated becomes unduly early, which is likewise undesirable. (Refer to FIG. 1D.) When the timing at which the application of the brake pulse starts or the timing at which the application of the kick pulse terminates changes greatly in this way, the brake or the kick is applied too severely. Because of this, a prior art type optical disk device of the type described above may become unable to transition to a state in which focus servo control is performed upon the second layer. In the worst case, there is also a fear that the objective lens may come into collision with the recording surface of the optical disk, which is extremely undesirable.
Accordingly, with such a prior art type optical disk device, if an inter-layer offset such as described above occurs, there is the problem that it cannot smoothly transition from a state in which its pickup is reading out information recorded upon the first layer of the disk, to a state in which the pickup reads out information recorded upon the second layer of the disk. Since, in the worst case, with such a prior art type optical disk device, there is also a fear that the objective lens may undesirably come into collision with the recording surface of the optical disk, accordingly there is also the problem that damage to the objective lens, and/or damage to the optical disk, may take place.
The object of the present invention is to provide an optical disk device which is capable of transitioning smoothly between a state in which it is reading out information recorded on the first layer and a state in which it reads out information recorded on the second layer, even if an offset is present between the layers.